The present invention relates to a novel corrosion-resistant composite oxide material or, more particularly, a corrosion-resistant material of which at least the surface layer is formed from a sintered body of a unique composite oxide having extremely high corrosion resistance against an atmosphere of a halogen-containing corrosive gas or a plasma of such a gas.
As is well known, the manufacturing process of various semiconductor devices involves a step of dry etching or a dry-process formation of a thin film on a substrate surface which is conducted sometimes by using a highly reactive and highly corrosive halogen-containing gas such as chlorine- and/or a fluorine-containing gas, referred to as a processing gas hereinafter, in a chamber for plasma generation in some cases.
In consideration of the good corrosion resistance of the material, a silica-based material or silicon carbide-based material is used as a material for forming parts of the plasma instrument or apparatus coming into contact with such a highly corrosive atmosphere including, for example, inner walls of the plasma chamber and various jigs such as holders to support a semiconductor silicon wafer, protective covers, insulation rings and the like.
Along with the increase of demand in recent years for a higher and higher degree of integration in semiconductor devices, the process of dry etching and/or thin-film formation is conducted, as a recent trend, by using a halogen-containing processing gas which is more reactive and hence more corrosive than the processing gases used before.
The shift of the processing gas toward more corrosive ones necessarily causes a problem that the apparatus walls and tools made from a silica-based or silicon carbide-based corrosion-resistant material can no longer withstand the attack of the atmosphere of such a processing gas having increased corrosiveness resulting in serious troubles in connection with the performance of the instrument or apparatus due to degradation of the surface nature such as, for example, a decrease in the transparency consequently decreasing the yield of acceptable products.
With an object to solve the above mentioned problems, a proposal is made in Japanese Patent Kokai 10-45461 for the use of certain composite oxide materials such as yttrium aluminum garnet of the composition formula Y.sub.3 Al.sub.5 O.sub.12 and silicate compounds as a corrosion-resistant material capable of withstanding the halogen-containing processing gases and plasmas thereof having increased corrosiveness.
These newly proposed corrosion-resistant materials still have a problem that, due to the very high melting point of the materials, a corrosion-resistant sintered body of the material cannot be prepared unless the sintering temperature is increased so high as to cause a heavy increase in the manufacturing costs of the sintered material.
An alternative proposal is made also in Japanese Patent Kokai 10-45461 for the use of a fluoride compound as the constituent of a corrosion-resistant material as a whole which should withstand the attack of a halogen-containing corrosive gas such as fluorine-containing gases.
When a corrosion-resistant material is formed from a mixture of fluoride compounds according to the above mentioned proposal, such a material cannot be used at a temperature of several hundreds centigrade or higher because the melting point of such a fluoride mixture is so low. When a single kind of a fluoride compound such as yttrium fluoride is used as a material for forming a corrosion-resistant material, the fluoride compound is converted into the corresponding oxyfluoride at a temperature of 1000.degree. C. or higher in the presence of even a trace amount of oxygen in the atmosphere so that full corrosion resistance can no longer be exhibited under such conditions.